CDC Warning on Misuse of Pest Strips

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CDC Warning on Misuse of Pest Strips

Image: Black County Museums/

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Every week, the US Centers for Disease Control (CDC) publishes a Morbidity and Mortality Weekly Report (MMWR). It's meant mostly for doctors, public health practitioners, epidemiologists, and other scientists. It's not something you read over dinner for light entertainment. Unless, you know, you're a bug nerd like me.

Dichlorvos-impregnated strips (2,2-dichlorovinyl dimethyl phosphate, or DDVP pest strips) were first registered in 1954 under the trade name Vapona™ by Shell Chemical Company. These pest strips have been used by entomologists, museums, and other conservators for museum fumigation for decades.

DDVP is highly volatile, so does an excellent job of diffusing through an enclosed space. I'll repeat – Highly Volatile. A block of DDVP emits vapors that repel and kill insects within 1,200 cubic feet for up to 4 months. It's a strong smell that makes me nostalgic. It's the smell of museum specimens and unopened cabinets of curiosities. It's the smell of old insect collections.

DDVP kills insects so well because it is one of the last organophosphate pesticides still available for indoor use in the US. Organophosphates can be dangerous, and misuse can result in ending up on your back twitching like a dying roach.

Organophosphates kill bugs by preventing nerve cells from turning stimulating signals off. They block the enzyme acetylcholinesterase, which is present in all animal nervous systems. Overstimulating nerve cells this way leads to tremors, paralysis, and death. Fortunately, the amount of DVPP it takes to kill an insect is small compared to what it takes to cause symptoms in humans.

The critical safety element is how you use this pesticide. The CDC Report suggests that's where the problem lies. Thirty-one cases were reported to The National Institute for Occupational Safety and Health (NIOSH) sentinel system of acute dichlorvos pest strip–related illness between 2000 and 2013. That might not seem like a lot, but in the words of the study lead author, Dr. Rebecca Tsai, "it's definitely an underestimate of what is happening." The sentinel system has just 12 participating U.S. states. Of that small subsample of states, only those cases reported to State Public Health Departments are known about by the CDC.

Twenty (65%) of the 31 cases involved using DDVP incorrectly and in violation of the instructions and safety labels. As someone who's been trained to only use DDVP with eye protection, gloves, and a respirator if in an enclosed space, this is chilling to read:

"The majority of these illnesses resulted from use of the product in commonly occupied living areas (e.g., kitchens and bedrooms), in violation of label directions.... Contributing factors other than using strips in occupied areas included excessive application, placing strips in sealed bags to treat infested items, lack of skin protection (e.g., gloves or prompt skin washing), placing strips in closets and pantries, cutting and tearing strips into smaller pieces, and using a heater and fan to accelerate vapor dissemination from strips."

The CDC suggests that part of the reason for misuse of DDVP strips relates to confusing packaging. This photo shows two over-the-counter DDVP containing products that Americans can buy at most large box retail stores:

Two Dichlorvos containing products available to any consumer–but with very different uses.

The first package is typical of the main use of this compound: for hanging up in places where there are no humans, or using in sealed compartments. It does has a graphic on the back showing visually that it's not meant to be used in living spaces. Or at least not around a television.

The instructions on the DVPP bed bug package say to seal the pest strips in the bag with the mattress for a week to make sure the bugs are gone. The back of the package has a lot of instructions in tiny print. "Do not use in areas where people will be for extended periods of time" is pretty vague. How long is "extended"? If you are bagging up your bed or furniture, probably a lot less time than you usually spend in your bedroom.

Bed bugs were clearly the motivation for some unwise uses of DDVP. Having read and discussed some of the case reports, I'm a little amazed there were not more serious injuries. I agree with the CDC that better packaging and labeling would be helpful in making sure that people use DDVP with appropriate caution.

If it were up to me, I'd at least have something along the lines of "FOR THE LOVE OF GOD DON'T TOUCH THIS STUFF WITHOUT GLOVES" on the packaging. There should be a way to more clearly indicate that this compound has a track record of neurological damage and is a Group B2 probable human carcinogen.

The other part of the label that ought to change are stronger instructions to only work with this material in well-ventilated areas. The thing that lets DDVP kill is building up a vapor pressure–basically, having a high concentration of the nasty stuff in the air. You can put DDVP in a small, enclosed space–but then you have to leave and not breathe any of it.

In the United States, DDVP is still available over the counter and for use in the home. DDVP has been restricted use only in the European Union since 2002.

DDVP has been under investigation by the EPA for decades. EPA referred DDVP to Special Review process in 1980 because of studies suggesting DDVP was carcinogenic and neurotoxic. For the next 10 years, DDVP sat in Special Review, and nearly all of its uses on food products were revoked. In 1995, Amvac, the new owner of the trademark, voluntarily cancelled use of Vapona in foggers, aerial applications, and food manufacturing. After that, things get a bit murky. In 2007, EPA removed DDVP from Special Review. Several different non-profits, including American Bird Conservancy and Natural Resources Defense Council, protested. In 2008, use of DDVP in dog flea collars was discontinued voluntarily. And now, some new uses of DDVP are being added as a bed bug fumigation agent.

I covered another CDC Morbidity and Mortality report recently that found hundreds of injuries due to misuse of pesticides in attempts to control bed bugs. The problem there, as here, is two-fold.

And that leads me to the second problem: income. If you are low income, you are more likely to have a pest problem, and less likely to be able to afford professional pest control. You may not have a smart phone or computer that will let you access or find available resources. And that is why funding for State Extension and Outreach and Public Health Services is important to all of us.

While the CDC reported the problem, it's the US EPA (Environmental Protection Agency) that actually regulates pesticide sales and labels. Any changes as a result of this report (and the earlier one about bed bugs) must come via EPA. New and clearer packaging initiatives have been promoted by the EPA in the past, so here's hoping they continue that great trend.